The present invention relates to an X-ray tomography apparatus which displays tomographic images having less influence over artifacts such as a cone-beam artifact, a windmill artifact, etc., at an X-ray CT (Computed Tomography) apparatus or the like, and an artifact reducing method thereof.
In a multi-slice X-ray computer tomography (X-ray CT) apparatus, the number of slices is now increasing to 64 or 256. There have been known various cone-beam image reconstruction algorithms using a helical scan of the X-ray CT apparatus. However, one problem common among the cone-beam image reconstruction algorithms is that a sampling interval in a body-axis direction (called also z direction or slice direction) of a subject is insufficient. These algorithms run counter to Nyquist's theorem and cause vertical windmill-like artifacts within each reconstructed image due to high-frequency components. That is, when the resolution of a detector is insufficient for a structure and a helical pitch is made larger at the helical scan, interpolation calculations cannot be carried out ideally and hence the windmill-like artifacts occur on an image.
In order to reduce such windmill-like artifacts, multi-point interpolation is performed in the z direction to reduce the width of a fluctuation of a target signal, thereby casting the windmill-like artifacts into the shade. In Japanese Unexamined Patent Publication No. 2003-325502, for example, an interpolation process is performed in a z direction upon execution of a reconstruction function convolution process thereby to attempt to reduce windmill-like artifacts.